JP2007336547A - Wireless system, base station device and terminal device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that it has not been known how to determine the number of beams applied to simultaneous transmission since beam interference occurs and signal quality is deteriorated in orthogonal random beam forming ORBF when the number of transmission beams is increased. <P>SOLUTION: Each terminal device receives a pilot signal transmitted from a base station by a random beam and reports an identifier of a beam with highest signal to interference noise ratio (SINR) and a value of the SINR of that signal to the base station. On the basis of report information from the terminal device, the base station determines the number of transmission beams for maximizing system capacity and transmits data destined to terminals. The number of transmission beams is determined for the unit of a radio frame or for the unit of a plurality of radio frames. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a radio system including a base station apparatus and a plurality of terminal apparatuses, a base station apparatus, and a terminal apparatus, and more particularly, to a beam forming method in multiuser MIMO transmission performed in the radio system, The present invention relates to a radio system, a base station apparatus, and a terminal apparatus that realize a transmission method with high frequency utilization efficiency by suppressing unnecessary transmission in a random beamforming system.

Various researches related to MIMO (Multi-Input Multi-Output) transmission are in progress.
Non-Patent Document 1 shows that frequency use efficiency can be greatly improved in single user MIMO in which a base station and a terminal perform MIMO transmission on a one-to-one basis. Dirty paper coding (DPC) is introduced in Non-Patent Document 2, and Non-Patent Document 3 and Non-Patent Document 4 report that if DPC is applied, the maximum capacity of MIMO broadcast transmission is reached. Yes. However, DPC is difficult to implement in a wireless system due to the large amount of calculation.

  On the other hand, Non-Patent Document 5 introduces Block Diagonalization (BD). Here, the base station performs linear space precoding and performs zero forcing on the inter-user interference. Non-Patent Document 5 is based on the premise that Channel State Information (CSI) can be estimated ideally. However, in actual implementation of MIMO, ideal estimation becomes difficult especially when the number of antennas and the number of users are large. It is known. Further, when trying to transmit complete CSI information, an increase in the amount of feedback information becomes a problem.

  Non-Patent Document 6 and Non-Patent Document 7 propose multi-user MIMO using partial CSI. However, in these existing technologies, the number of transmitting antennas and the number of receiving antennas are the same, and it cannot be said that the condition setting is adapted to the cellular environment.

  Non-Patent Document 8 proposes a method of using only a signal-to-interference noise ratio (SINR) called “Random Beamforming” as feedback information. Here, random beamforming is used, and resource allocation is performed only for one user in the best propagation path environment.

  Furthermore, Non-Patent Document 9 proposes application of random beamforming to MIMO. This method is a method corresponding to MIMO of a single user because resources can be allocated to only one user at the same time.

  Non-Patent Document 10 introduces orthogonal random beam forming (ORBF) using orthogonal Random beamforming. In the ORBF, each user terminal reports a beam index that maximizes a signal-to-interference and noise ratio (SINR) to the base station. In ORBF, it is known that the maximum total capacity of the DPC is reached when the number of users is large. However, in the cellular system, since the number of users of each base station is about 64 users at most, it is considered that only a slight performance gain can be obtained even if ORBF is applied.

  Therefore, in Non-Patent Document 11, improvements are made by a method called MUDAM (Multi-user diversity and multiplexing). However, MUDAM needs to feed back CSI many times before deciding all beamform vectors, and is not suitable when the user terminal moves at high speed as in a cellular system.

G.J.Foschini and M.J.Gans, “On limits of wireless communications in a fading environment when using multiple antennas”, Wireless Personal Commun .: Khuwer Academic Press, no. 6, pp. 311-335, 1998. M. Costa, “Writing on Dirty Paper”, IEEE Trans. Inf. Theory, Vol. 29, pp. 439-441, May 1983. P. Viswanath and D. Tse, “Sum capacity of the Vector Gaussian broadcast channel and uplink-downlink duality”, IEEE Trans. Info. Theory, vol. 49, pp. 1912-1921, Aug. 2003. G. Carie and S. Shamai, “On the achievable throughput of a multiantenna Gaussian broadcast channel”, IEEE Trans. Info. Theory, Vol. 49, pp. 1691-1706, Jul. 2003. Q.H.Spencer, A.L.Swindehurst and M.Haardt, “Zero-forcing Methods for Downlink Spatial Multiplexing in Multi-User MIMO Channels”, IEEE Trans. Sig. Proc., Vol. 52, pp. 461-471, Feb. 2004. RWHeath Jr., M. Airy and AJPaulraj, “Multiuser diversity for MIMO wireless systems with linear receivers”, in Proc. Of Asilomar Conf. On Signals, Systems, and Computers, vol. 2, pp. 1194-1199, Nov . 2001. H. Lee, M. Shin and C. Lee, “An eigen-based MIMO multiuser scheduler with partial feedback information”, IEEE commun. Lett., Vol. 9, pp. 328-330, Apr. 2005. P. Viswanath, D.N.C.Tse and R. Laroia, “Opportunistic beamforming using dumb antennas”, IEEE Trans. Inform. Theory, vol. 48, pp. 1277-1294, Jun. 2002. J.Chung, C.S.Hwang, K.Kim and Y.K.Kim, “A random beamforming technique in MIMO systems exploiting multiuser diversity”, IEEE J. Select. Areas Commun., Vol. 21, pp. 848-855, Jun. 2003. M. Sharif and B. Hassibi, “On the capacity of MIMO broadcast channels with partial side information”, IEEE Trans. Info. Theory, vol. 51, pp. 506-522, Feb. 2005. GCBriones, AADowhuszko, J. Hamalainen and R. Wichiman, “Achievable data rates for two transmit antenna broadcast channels with WCDMA HSDPA feedback information”, Proc. IEEE Int. Conf. Commun., Vol. 4, pp.2722-2727 , May 2005.

  In conventional ORBF (Orthogonal Random Beam Forming), the number of random beams is a fixed value. In random beam transmission, when the number of beams transmitted simultaneously increases, interference occurs between the beams, resulting in signal quality degradation. Therefore, simultaneous signal transmission using a large number of random beams does not always lead to maximization of the system capacity. This is the first problem to be solved by the present invention. Conventionally, it has not been known how to determine the number of beams to be transmitted simultaneously. This is the second problem to be solved by the present invention.

  In the present invention, in order to solve the first problem, the base station can vary the number of random beams so as to maximize the system capacity according to the radio reception status reported from the terminal device. Incorporates a control mechanism. Specifically, in the present invention, each terminal apparatus receives a pilot signal transmitted by a random beam from a base station, and a signal-to-interference and noise rate (SINR) S / (I + N) Report the identifier of the highest beam and the SINR value of that beam to the base station. The base station includes beam number determination means for obtaining the number of transmission beams that maximizes the system capacity based on the report information from the terminal device. The beam number determining means determines a transmission beam number, a used beam, and a communication partner terminal that transmits data using the transmission beam. The determination of the number of transmission beams is performed in units of radio frames or in units of a plurality of radio frames.

  In order to solve the second problem, the present invention introduces an MBS (Multi Beam Selection) algorithm for determining the number of transmission beams and beams based on SINR information reported from a terminal. When the signal to noise rate (SNR) is low, interference does not become a dominant term that determines signal quality, and the system capacity increases when a plurality of beams are transmitted simultaneously. On the other hand, when the SNR is high, since interference becomes the dominant term, transmission with a single beam is performed instead of transmission with a plurality of beams. In a MIMO environment where a terminal has multiple antennas, transmission is performed with one stream including the antennas. Thus, by determining the number of transmission beams by the MBS algorithm, the number of beams can be determined adaptively, and the second problem can be solved.

  According to the present invention, it is possible to keep the number of transmission beams of random beams, which could not be performed because the procedure for changing the number of transmission beams is not clear, in an optimum state, and keep the system capacity at a maximum.

A first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 shows a configuration example of a MIMO (Multi-Input Multi-Output) transmission system in a cellular environment assumed by the present invention. The base station side has m _t antennas, and the terminal side has m _r antennas. The propagation path 2 is a MIMO channel, and each antenna receives fading independent of each other.

A signal transmitted from the base station is subjected to random beam formation by a random complex unitary beamforming matrix consisting of m _t × m _t . In a cellular environment, if the number of users is K, there is generally a relationship of K> m _t > m _r . In the prior art, is a relationship of m _{b =} m _t the transmission beam number, in the embodiment of the present invention, in most cases, holds the relationship of m b _{<m t,} only if the average SNR of each terminal is low , the relationship of _m b = _{m t} is established.

  Hereinafter, a theoretical formula for evaluating the performance of the embodiment of the present invention is derived. A MIMO channel consisting of a transmission channel from a transmitting antenna i to a receiving antenna j

と表記する。ここでは、送信アンテナ番号ｉからユーザｋの受信アンテナ番号ｊへの伝送チャネルｈ_ｉｊ（ｋ）は、複素ガウス・ランダムチャネルと仮定する。送信機は、ｍ_ｂの互いに直交するランダムベクトルΦｍからなるアレイ重みを使ってビーム形成を行う。

Is written. Here, the transmission channel h _ij (k) from the transmission antenna number i to the reception antenna number j of the user k is assumed to be a complex Gaussian random channel. The transmitter performs beamforming using array weights consisting of random vectors Φm mutually orthogonal in m _b.

The received signal y _k of the user k is

で表記される。ここで、Ｓ_ｍはｍ番目の送信信号を表す。送信ビームの電力は、等配分されると仮定すると、

It is written with. Here, S _m represents the m-th transmission signal. Assuming that the transmit beam power is equally distributed:

となる。ここで、ρ₀は平均ＳＮＲを示す。

It becomes. Here, ρ ₀ represents an average SNR.

First, consider the case of m _r = 1. Assuming complete CSI (Channel State Information), the terminal k can calculate the SINR value SINR _km of the m-th beam by the following equation.

全端末が、受信したビームの内で最も高いＳＩＮＲの値を基地局に報告し、基地局が、その内からＳＩＮＲが最も高いｍ_ｂの端末を選択してビーム送信したとすると、システム容量Ｒ(ｍ_ｂ)は、次式で近似できる。

When all terminals, and report the value of the highest SINR among the received beams to the base station, the base station, and the beam transmitted by selecting a terminal of highest m _b is SINR from among the system capacity R (m _b ) can be approximated by the following equation.

ここで、Φｍが複素ガウスランダム変数であり、ｋやｍに対してユニタリー変数であることを考えると、SINR_ｋｍの値は、次式で近似できる。

Here, considering that Φm is a complex Gaussian random variable and is a unitary variable with respect to k and m, the value of SINR _km can be approximated by the following equation.

ここで、ｚやｙは、それぞれｘ^２（２）分布およびｘ^２（２ｍ_ｂ−２）分布に従う。

Here, z and y are each ^x 2 (2) distribution and ^x 2 _(2m b -2) according to the distribution.

Cumulative distribution function (CDF) F _S (x) of SINR _km

となる。

It becomes.

Thus, a _{m b} at the time of transmission system capacity R _{(m b),} the optimum value of the transmission beam number _{m b} is as follows.

例えば、低ＳＮＲの場合には、ρ₀＝０、ｕ＝Ｆ_ｓ ^Ｋ（ｘ）とすれば、

For example, in the case of a low SNR, if ρ ₀ = 0 and u = F _s ^K (x),

となる。よって

It becomes. Therefore

となり、送信ビーム数が多い場合にシステム容量が最大となる。

Thus, the system capacity is maximized when the number of transmission beams is large.

On the other hand, in the case of a high SNR, assuming that ρ ₀ = infinity, the system capacities R (m _b ) and R (1) are as follows.

よって、送信ビーム数ｍ_ｂの最適値は、

Therefore, the optimum value of the transmission beam number m _b is

となる。

It becomes.

From the above study results, optimal m _b are seen to be different depending on the SNR. That is, when the SNR is low, the system capacity increases as the number of simultaneous transmission beams increases. On the other hand, when the SNR is high, the single beam transmission is superior in terms of system capacity.

  The combination {B, U} of the transmission beam and the destination user is

で得られる。

It is obtained by.

FIG. 2 is a sequence diagram showing a communication sequence between a base station device (Base station) and a terminal device (Terminal).
First, the base station, for each specified time slot, and transmits a pilot signal of a random m _t present (step 201). Terminal device, based on the pilot information report, estimates the signal-to-interference noise ratio SINR _miles of each beam, and the maximum value of the SINR _miles, the beam identifier SINR _miles is the maximum value (ID) to the base station apparatus (Step 202).

  In the base station apparatus, a combination of a beam to be transmitted and a transmission destination user is determined from information indicating the obtained maximum SINR using (Equation 15), and an allocation channel (frequency and timing) to the terminal apparatus is determined. The result is determined and the result is notified to the terminal device (step 203). The base station apparatus transmits data for the corresponding user as a radio signal at the frequency and timing specified in step 203. The terminal apparatus receives the signal addressed to the corresponding terminal apparatus transmitted from the base station apparatus at the frequency and timing designated in step 203 (step 204).

The radio apparatus (base station and terminal) of the present invention performs a transmission / reception operation on a slot basis composed of specific time slots. The weight of the random beam is updated for each slot, and a new beam weight is applied to the transmission signal.
As an example of how to create beam weights, a method using Schmidt's orthogonalization is generally used, and m _t −1 random vectors (m _t × 1) are prepared by random numbers, and Schmidt's orthogonalization algorithm is used. using, to generate a m _t number of independent weight vector.

Figure 3 is a diagram showing a state in which separate m _t pieces of beams for each slot is created by hatching features. Since orthogonalization of random numbers and Schmidt is used, the beam weight changes for each slot, resulting in a random beam both in time and space. For practical use, antenna weights of a kind that can be regarded as sufficiently random may be calculated in advance and stored in a table format in the memory of the base station apparatus. If the antenna weight value for each slot is searched from the above table, it is not necessary to generate a random number for each slot and perform the Schmidt orthogonalization operation.

FIG. 4 is a block configuration diagram showing the configuration of the base station apparatus.
A pilot signal transmitted for channel estimation is generated by pilot signal generation section 104. The generated pilots are subjected to spatial weighting by the spatial modulation unit 105 and become a spatially modulated pilot signal. Transmission data (user data) extracted from the network by the network interface 101 is modulated in the modulation unit 102 in accordance with a modulation scheme (MCS) instructed by the resource manager 109. The modulated information is converted into a spatially modulated signal by integrating the array weights in the weight integrating unit 103.

  The spatially modulated transmission data signal is time-multiplexed with the pilot signal spatially modulated by the spatial modulation unit 105 in the signal synthesis unit 106. The transmission signal output from the signal synthesis unit 106 is converted from a baseband signal to an RF signal in an RF unit (not shown in FIG. 4), and transmitted from the antenna via the demultiplexer 107.

  Information on SINR transmitted from the terminal is received by the antenna, passed through the demultiplexer 107, converted into a baseband signal by an RF unit not shown in FIG. Demodulation section 108 extracts SINR information from the received signal and sends the SINR information to resource manager 109. The resource manager 109 determines the transmission beam and the transmission destination user from the SINR information of a plurality of users according to the algorithm shown in (Equation 15), and also determines the MCS to be transmitted from the estimated SINR obtained at that time.

FIG. 5 is a configuration diagram illustrating a block configuration of the terminal device.
The pilot signal transmitted from the base station apparatus is received by the antenna, and is input to the demodulation unit 302 via the deplexer 301, and SINR is estimated. The estimated SINR value output from the demodulator 302 is input to the resource manager 303. The resource manager 303 compares the SINR for each beam and selects the beam having the maximum SINR. The maximum SINR value and the identifier (beam ID) of the beam having the maximum SINR value are output from the resource manager 303 to the modulation unit 305. The modulation unit 305 modulates the SINR and the beam ID according to a prescribed modulation scheme.

  The modulated signal is converted from a baseband signal to an RF signal by an RF unit (not shown in the figure), and then transmitted from the antenna via the demultiplexer 301. The downlink data signal transmitted from the base station apparatus is input to the demodulation unit 302 via the deplexer 301, and the demodulated data is transmitted to the network via the network interface 304.

  According to the above communication procedure and apparatus configuration, the number of random beams can be adaptively changed, so that the first problem described above is solved. Further, since the number of beams to be transmitted simultaneously can be determined by (Equation 15), the second problem described above is also solved.

  In the above embodiment, the type of modulation scheme is not particularly limited, but CDMA or OFDMA can be applied as the primary modulation scheme, for example. As the secondary modulation scheme, a general modulation scheme such as QPSK or 16QAM can be applied.

  In FIG. 2, as shown in step 203, the channel assignment result is notified to the terminal device after channel assignment, but the channel assignment result notification sequence is omitted and each terminal device is blinded. You may make it receive transmission data.

  In the case of a terminal device equipped with a plurality of antennas, a plurality of streams can be transmitted simultaneously. In this case, the terminal device needs to increase the number of SINRs reported to the base station device. However, when a logically configured channel is considered as another terminal, the algorithm of (Equation 15) can be applied as it is.

  For example, the resource management unit predetermines a predetermined number X equal to or less than the number of reception antennas, selects X beams in descending order of the SINR value from the SINR measurement result or estimation result, and the modulation unit The identifier of X beams selected by the resource management unit and the SINR value of each beam may be transmitted to the base station. In this case, since a plurality of streams can be transmitted at the same time, the transmission rate of the terminal apparatus can be significantly increased due to the multi-channel transmission effect in MIMO. In addition, the terminal device may be devised to combine signals received by a plurality of antennas with an appropriate signal combining unit to improve signal quality.

  ADVANTAGE OF THE INVENTION According to this invention, when implementing random beamform by cellular communication, it becomes possible to determine the optimal number of transmission beams according to the propagation environment of an electromagnetic wave, and to maximize the capacity of a system.

The figure of the radio | wireless system containing the base station apparatus which shows one Example of this invention, and a terminal device. The figure which shows one Example of the communication sequence between the base station apparatus and terminal device in this invention. The figure for demonstrating the transmission method of the random beamform in this invention. The block diagram which shows one Example of the base station apparatus applied to this invention. The block diagram which shows one Example of the terminal device applied to this invention.

Explanation of symbols

1: base station apparatus, 2: MIMO transmission path, 3: terminal apparatus, 4: base station antenna, 5: terminal antenna, 101: network interface, 102: modulation section, 103: weight integration section, 104: pilot signal generation section , 105: spatial modulation unit, 106: signal synthesis unit, 107: deplexer, 108: demodulation unit, 109: resource manager, 301: deplexer, 302: demodulation unit, 303: resource manager, 304: network interface, 305: modulation unit .

Claims (8)

A wireless system comprising a base station device having a plurality of antennas and a plurality of terminal devices,
One or more terminal apparatuses receive the pilot signal in the form of a random beam transmitted from the base station apparatus, and the detection result of the signal to interference and noise ratio (SINR) of each beam is described above. Report to the base station equipment,
The base station apparatus determines a number of beams to be applied to data transmission addressed to the terminal apparatus based on the SINR reported from the terminal apparatus. The radio system according to claim 1,
The radio system according to claim 1, wherein the base station apparatus determines the number of beams based on SINR reported from the terminal apparatus so that the system capacity is maximized. The radio system according to claim 1,
When the base station apparatus has a signal-to-noise ratio SNR (Signal to Noise Rate) substantially equal to SINR, the number of beams is made equal to the number of transmission antennas. When the SNR is sufficiently larger than SINR, the number of beams is 1 is a wireless system. A pilot generating unit that generates a plurality of array weights for orthogonal random beamforms, and adds the array weights to the pilot signals to create a random beamformed pilot signal;
A transmitter that transmits the pilot signal generated by the pilot generator to the terminal device;
A receiver that receives SINR (Signal to Interference and Noise Rate) information indicating a signal-to-interference and noise ratio of the pilot signal from the terminal device;
A resource management unit that determines the number of beams to be applied to data transmission to the terminal device based on the SINR information and a transmission beam;
A base station apparatus, wherein data is transmitted from the transmission section to the terminal apparatus using a beam selected by the resource management section. In the base station apparatus according to claim 4,
The base station apparatus, wherein the resource management unit determines the number of beams based on SINR information received from the terminal apparatus so that the system capacity of the entire base station apparatus is maximized. In the base station apparatus according to claim 4,
When the signal-to-noise ratio SNR (Signal to Noise Rate) substantially matches the SINR, the number of beams is made to match the number of transmission antennas, and when the SNR is sufficiently larger than the SINR, the number of beams is set to 1. Base station apparatus. An SINR detection unit that receives a plurality of random beamformed pilot signals transmitted from the base station apparatus and measures or estimates a signal to interference and noise ratio (SINR) of the pilot signals;
A resource management unit that selects a beam having the highest SINR based on the SINR of each beam measured or estimated by the SINR detection unit;
A terminal apparatus comprising: a modulation unit for transmitting the beam selected by the resource management unit and the SINR value of the beam to the base station as a modulation signal. The terminal device according to claim 7,
A plurality of receiving antennas for performing MIMO reception;
The resource management unit predetermines a predetermined number X equal to or less than the number of the receiving antennas, and selects X beams in descending order of SINR values from the SINR measurement result or estimation result,
The terminal device, wherein the modulation unit transmits the identifiers of X beams selected by the resource management unit and the SINR value of each beam to the base station.

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